The present invention relates generally to camera bodies, and particularly to a camera body formed of plastic with a reinforcing metal plate inserted therein.
Recently, it has been considered to form a camera body of plastic in order to cut down on the weight and the price of the camera. However, such construction poses problems in maintaining dimensional stability and strength.
Specifically, since the distance betweeen the plane of the camera film guide rail and the plane of the seat of the lens mount or "flange back" is a predetermined value, it is necessary that a plastic camera body have sufficient strength for accurately maintaining the position of the flange back relative to the film guide rail. However, when the camera body is formed of plastic, it is often impossible to provide the plastic body with sufficient thickness to meet this strength requirement.
Particularly in the case of a single lens reflex camera, when the thickness of its aperture portion is increased for strengthening purposes, the camera as a whole becomes quite large, contrary to the intended purpose of realizing a compact and lightweight camera. In fact, it is often impossible to provide the plastic body of sufficient thickness.
As a result, it has been proposed in U.S. Pat. No. 4,067,032 that the part whose strength must be maintained, namely, the part having the aperture therein, which determines the picture size and the plane of the film guide rail, be made separately of metal, while other parts are formed of plastic in order to guarantee sufficient strength of the camera body. In accordance with U.S. Pat No. 4,067,032, accurate positioning of the flange back is ensured by connecting a metal bracket or plate inserted in the camera body directly with a metal front plate unit extending in the plane of the lens mount.
When a metal plate is inserted into a camera body formed of plastic, the metal plate must necessarily have a connecting portion for interengaging the plastic. The metal plate is usually bent several times in alternate directions for the sake of appearance, light blockage and strength, while the connecting portion, which is located in the vicinity of the film spool chambers, becomes visible only when the user opens the back cover. Any plastic flash or gaps formed at the connecting portion of the plate are thereby maintained normally out of sight. To eliminate unsightly plastic flash, gaps, and the like where the metal plate is connected with the plastic body, it will be understood that it is essential to eliminate any clearance between the metal plate and the molds which are used to mold the camera body by keeping the dimensional tolerances of the metal plate and the molds as high as possible.
However, it is extremely difficult to maintain tolerances of a metal plate consisting of, for example, die cast aluminum, within .+-.0.1 mm, when a large number of molds for the metal plates and a large number of molds for the entire camera body are used in large scale production. It is also difficult to check continually for the above-mentioned clearance when the molds for the metal plate are interchanged among each other and the molds for the camera body are also interchanged among each other. Consequently, it is difficult, if not impossible, to guard against this clearance so that molten plastic does not flow or seep into the clearance when the camera body is molded. When such clearance exists, the molten plastic will seep into it and thereby form plastic flash on the surface of the finished camera body.
Further, during the molding of a camera body of plastic with a metal plate inserted in the plastic, there is the danger that a gap will form at the connecting portion of the metal plate with the plastic body due to differences between physical properties such as thermal expansion coefficients as the camera body cools. Such gaps are undesirable for the sake of appearance, and they create the danger of light leakage.
An object of the present invention is to eliminate the above-mentioned shortcomings in the prior art by providing a camera body of molded plastic with a metal plate inserted in the plastic body, the metal plate having at least one projection at each of its portions which connect to the plastic body where the projections contact the molding surface of the body mold in response to molding pressure, thereby preventing molten plastic from seeping into any clearance between the plate and the molding surface.
Another object of the present invention is to locate the connecting portions of the metal plate with the plastic body within planar regions of the camera body.
A further object of the present invention is to improve the adhesion of the metal plate to the plastic body by providing projections at edges of the connecting portions of the metal plate.
In accordance with the present invention, a camera body comprises a plastic body formed in a molding operation including a central portion, a film loading chamber and a film windup chamber each located at opposite ends of the central portion, and a metal plate fixed in the plastic body for reinforcing it, the metal plate having at least one connecting portion for interengaging with the plastic body. At least one projection extends from each connecting portion for contacting a molding surface in response to pressure applied to the projection when the camera body is molded to prevent seepage of molten plastic between the metal plate and the molding surface, thereby preventing formation of plastic flash.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described perferred embodiments of the invention .